Hitachi MK-97DF8018-00 User manual

Brand: Hitachi

Model: MK-97DF8018-00

Category: Software

Type: User manual

This manual is also suitable for

Copy-on Write SnapShot

Product Version

Document Organization

Getting Help

Table of Contents

AST

IND

INKS

MK-97DF8018-00

Hitachi Simple Modular Storage Copy-on-

Write SnapShot User’s Guide

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Notice: No part of this publication may be

reproduced or transmitted in any form or by

any means, electronic or mechanical, including

photocopying and recording, or stored in a

database or retrieval system for any purpose

without the express written permission of

Hitachi Data Systems Corporation (hereinafter

referred to as “Hitachi Data Systems”).

Hitachi Data Systems reserves the right to

make changes to this document at any time

without notice and assumes no responsibility

for its use. Hitachi Data Systems products and

services can only be ordered under the terms

and conditions of Hitachi Data Systems'

applicable agreements. All of the features

described in this document may not be

currently available. Refer to the most recent

product announcement or contact your local

Hitachi Data Systems sales office for

information on feature and product

availability.

This document contains the most current

information available at the time of

publication. When new and/or revised

information becomes available, this entire

document is updated and distributed to all

registered users.

Hitachi Data Systems is a registered

trademark and service mark of Hitachi, Ltd.,

and the Hitachi Data Systems design mark is a

trademark and service mark of Hitachi, Ltd.

Other company and product names mentioned

herein are trademarks of their respective

companies. Mention of third-party products is

for informational purposes only and

constitutes neither an endorsement nor a

recommendation. Hitachi Data Systems

assumes no responsibility with regard to the

performance or use of these products.

Preface iii

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Preface

This document provides instructions on assessing your snapshot

requirements, designing an implementation to meet those

requirements, and implementing and operating Copy-on-Write

Snapshot software using the Storage Navigator 2 graphical user

interface.

This preface includes the following information:

• Document Revision Level

• Safety and Warnings

• Product Version

• Release Notes

• Referenced Documents

• Document Conventions

• Convention for Storage Capacity Values

• Getting Help

• Comments

Notice: The use of the Hitachi Simple Modular Storage 100and

all Hitachi Data Systems products is governed by the terms of

your agreement(s) with Hitachi Data Systems.

iv Preface

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Document Revision Level

This section provides a history of the revision changes to this document.

•

Safety and Warnings

This document uses the following symbols to draw attention to important

safety and operational information. The Danger, Electric Shock, and ESD

symbols are included only in hardware manuals.

•

Intended Audience

This document is intended for users with the following background:

• Background in data processing and understands RAID storage systems

and their basic functions.

• Familiarity with Hitachi Modular Storage systems.

• Familiarity with operating systems such as the Windows 2000, Windows

Server 2003 operating system, or UNIX.

Product Version

This document applies to Hitachi Simple Modular Storage 100 microcode

versions 1810/A and higher.

Release Notes

Make sure to read the Release Notes before enabling and using this product.

The Release Notes are located on the installation CD. They may contain

requirements and/or restrictions that are not fully described in this

document. The Release Notes may also contain updates and/or corrections

to this document.

Revision Date Description

MK-97DF8018-00 October 2007 Initial Release

Symbol Meaning Description

•

Tip Tips provide helpful information, guidelines, or suggestions for

performing tasks more effectively.

•

Note Notes emphasize or supplement important points of the main

text.

•

Caution Cautions indicate that failure to take a specified action could

result in damage to the software or hardware.

Preface v

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Document Organization

The following table provides an overview of the contents and organization

of this document. Click the chapter title in the first column to go to that

chapter. The first page of every chapter or appendix contains a brief list of

the contents of that section of the manual, with links to the pages where

the information is located.

•

Referenced Documents

These documents contain information that is related to the topics in this

document and can provide additional information about them.

• Hitachi Storage Navigator 2 Command Line Interface (CLI) User’s Guide

(MK-97DF8038), used to develop scripts.

• Hitachi Command Control Interface (CCI) software for Modular Storage

User's Guide (MK-97DF8016).

• Hitachi Storage Navigator Modular 2 program Help, which explains

SnapShot operations using the Navigator 2 GUI application.

Chapter/Appendix

Title

Description

Chapter 1, SnapShot

Overview

Provides descriptions of SnapShot components and how

they work together.

Chapter 2, Planning

and Design

Provides detailed planning and design information.

Chapter 3,

Requirements

Provides SnapShot requirements.

Chapter 4, Enabling

and Disabling

SnapShot

Provides instructions for enabling SnapShot.

Chapter 5,

Configuring

SnapShot

Provides detailed configuration and testing information.

Chapter 6, Using

SnapShot

Provides detailed information and procedures for using

SnapShot.

Chapter 7,

Monitoring and

Maintenance

Provides monitoring and maintenance information.

Chapter 8,

Troubleshooting

Provides information for correcting system problems.

Appendix A,

Operations Using CLI

Provides detailed Navigator 2 Command Line Interface

instructions for configuring and using SnapShot.

Appendix B,

SnapShot

Specifications

Provides SnapShot specifications.

Glossary Provides definitions for terms and acronyms found in this

document.

Index Provides locations to specific information in this document.

vi Preface

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Document Conventions

The following table describes the typographic conventions used in this

document.

•

Convention for Storage Capacity Values

Storage capacity values for hard disk drives (HDDs) in Hitachi Data

Systems’ storage products are calculated based on the following values:

• 1 KB = 1,000 bytes

• 1 MB = 1,000

bytes

• 1 GB = 1,000

bytes

• 1 TB = 1,000

bytes

Storage capacity values for hard disk drives (HDDs) in the Hitachi Simple

Modular Storage 100 are calculated based on the following values:

• 1 KB (kilobyte) = 1,024 bytes

• 1 MB (megabyte) = 1,024

bytes

• 1 GB (gigabyte) = 1,024

bytes

• 1 TB (terabyte) = 1,024

bytes

For further information on the Hitachi storage system, refer to the user's

guide for the system (for example, Hitachi Simple Modular Storage

Hardware Guide, MK-96DF8061).

Convention Description

Bold Indicates text on a window, other than the window title, including

menus, menu options, buttons, fields, and labels. Example: Click

OK.

Italic Indicates a variable, which is a placeholder for actual text provided

by the user or system. Example: copy source-file target-file. Note:

Angled brackets (< >) are also used to indicate variables.

screen/code

Indicates text that is displayed on screen or entered by the user.

Example: # pairdisplay -g oradb

< > angled

brackets

Indicates a variable, which is a placeholder for actual text provided

by the user or system. Example: # pairdisplay -g <group>

Note: Italic font is also used to indicate variables.

[ ] square

brackets

Indicates optional values. Example: [ a | b ] indicates that you can

choose a, b, or nothing.

{ } braces

Indicates required or expected values. Example: { a | b } indicates

that you must choose either a or b.

| vertical bar Indicates that you have a choice between two or more options or

arguments. Examples:

[ a | b ] indicates that you can choose a, b, or nothing.

{ a | b } indicates that you must choose either a or b.

underline Indicates the default value. Example: [ a | b ]

Preface vii

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Getting Help

If you have questions after reading this guide, contact an Hitachi Data

Systems authorized service provider[H1] or visit the Hitachi Data Systems

support website, http://support.hds.com.

Support Contact Information

If you purchased this product from an authorized Hitachi Data Systems

reseller, contact that reseller for support. For the name of your nearest

Hitachi Data Systems authorized reseller, refer to the Hitachi Data Systems

support web site for locations and contact information.

To contact the Hitachi Data Systems Support Center, please visit the Hitachi

Data Systems website for current telephone numbers and other contact

information. http://support.hds.com

Please provide at least the following information about the problem:

• Product name, model number, part number (if applicable) and serial

number

• System configuration, including names of optional features installed,

host connections, and storage configuration such as RAID groups and

LUNs

• Operating system name and revision or service pack number

• The exact content of any error message(s) displayed on the host

system(s)

• The circumstances surrounding the error or failure

• A detailed description of the problem and what has been done to try to

solve it

• Confirmation that the Hitachi Data Systems Hi-Track remote monitoring

feature has been installed and tested.

Comments

Your comments and suggestions to improve this document are greatly

appreciated. When contacting HDS, please include the document title,

number, and revision. Please refer to specific section(s) and paragraph(s)

whenever possible.

• E-mail: [email protected]

• Fax: 858-695-1186

• Mail: Technical Writing, M/S 35-10

Hitachi Data Systems

10277 Scripps Ranch Blvd.

San Diego, CA 92131

Thank you! (All comments become the property of Hitachi Data Systems

Corporation.)

viii Preface

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Contents ix

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Table of Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Document Revision Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Safety and Warnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Intended Audience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Product Version. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Release Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Document Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Referenced Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Document Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

Convention for Storage Capacity Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

Getting Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

1 SnapShot Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

Copy-on-Write SnapShot Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Hardware and Software Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

How SnapShot Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Volume Pairs—P-VOLs and V-VOLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

Data Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6

Differential Management LUs (DM-LU) . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6

Consistency Group (CTG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6

SnapShot Interface—Storage Navigator Modular 2 . . . . . . . . . . . . . . . . . . 1-6

2 Planning and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

The Plan and Design Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

Assessing Business Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

Establishing How Often a Copy Is Made (Copy Frequency) . . . . . . . . . . . . 2-2

Selecting a Reasonable Time Between Snapshots . . . . . . . . . . . . . . . . . 2-3

Establishing How Long a Copy Is Held (Copy Lifespan) . . . . . . . . . . . . . . . 2-3

x Contents

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Lifespan Based on Backup Requirements . . . . . . . . . . . . . . . . . . . . . . . 2-3

Lifespan Based on Business Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Establishing the Number of V-VOLs that Are Required. . . . . . . . . . . . . . . . 2-4

Establishing Data Pool Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

Measuring Workload Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5

Rule of Thumb Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8

Calculating Maximum Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Operating System Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

Identifying P-VOL and V-VOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

Cluster Software, Path Switching Software. . . . . . . . . . . . . . . . . . . . . . . 2-11

Microsoft Cluster Server (MSCS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Veritas Volume Manager (VxVM). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Windows 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Windows Server 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

Linux and LVM Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12

Windows Server 2003/Windows 2000 and Dynamic Disk . . . . . . . . . . . . . 2-12

3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

System Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

Supported Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

4 Enabling and Disabling SnapShot. . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

Enabling/Disabling SnapShot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

5 Configuring SnapShot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

Configuration Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

Assign Volumes for the Data Pool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

Notes on Adding a Data Pool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

Set Up the Virtual Volume (V-VOL) (manual method) . . . . . . . . . . . . . . . . . . . 5-3

6 Using SnapShot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

SnapShot Replication Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

Back Up Your Volume—Create a Pair. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

Using the Backup Wizard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

Create Pair Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

Update the V-VOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

Restore the P-VOL from the V-VOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

Restore from Tape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

Use the V-VOL for Tape Backup, Testing, Reports, Etc.. . . . . . . . . . . . . . . . . . 6-6

Edit Pairs, Data Pool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

Delete Pairs, V-VOLs, Data Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

Test the Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

Contents xi

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

7 Monitoring and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

Monitoring SnapShot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

Monitoring Pair Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

Monitoring Data Pool Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

Expanding the Data Pool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

Other Methods for Lowering Data Pool Load. . . . . . . . . . . . . . . . . . . . . . . 7-3

8 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

Pair Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2

Recovering from Pair Failure Due to POOL FULL . . . . . . . . . . . . . . . . . . . . 8-2

Recovering from Pair Failure Due to a Hardware Failure . . . . . . . . . . . . . . 8-2

Data Pool Capacity Exceeded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

A Operations Using CLI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

Enabling and Disabling SnapShot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

Operations for SnapShot Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3

Setting the POOL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-3

Setting the V-VOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

Performing SnapShot CLI Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5

Creating SnapShot Pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-5

Updating SnapShot Logical Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6

Restoring V-VOL to P-VOL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-6

Releasing SnapShot Pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-7

Changing Pair Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-8

Creating Pairs that Belong to a Group . . . . . . . . . . . . . . . . . . . . . . . . . . . A-8

Sample Back Up Script for Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-9

B SnapShot Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

General Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glossary-1

Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index-1

xii Contents

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

SnapShot Overview 1–1

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

SnapShot Overview

Snapshot creates virtual copies of data volumes within Hitachi

Simple Modular Storage systems. These copies can be used for

recovery from logical errors. They are identical to the original

volume at the point in time they were taken.

This guide provides instructions for planning and designing,

configuring and testing, and using and monitoring SnapShot. In

this chapter, see:

 Copy-on-Write SnapShot Software

 Hardware and Software Configuration

 How SnapShot Works

1–2 SnapShot Overview

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Copy-on-Write SnapShot Software

Hitachi’s Copy-on-Write Snapshot software creates virtual backup copies of

any data volume within the Simple Modular Storage systems with minimal

impact to host service or performance levels. These snapshots are suitable

for immediate use in decision support, software testing and development,

data backup, or rapid recovery operations.

SnapShot minimizes disruption of planned or unplanned outages for any

application that cannot tolerate downtime for any reason or that requires

non-disruptive sharing of data. Since each snapshot captures only the

changes to the original data volume, the amount of storage space required

for each Copy-on-Write Snapshot is significantly smaller than the original

data volume.

The most probable types of target applications for Copy-on-Write Snapshot

are:

• Database copies for decision support/database inquiries

• Non-disruptive backups from a Copy-on-Write Snapshot V-VOL

• Periodic point-in-time disk copies for rapid restores in the event of a

corrupted data volume

Hardware and Software Configuration

A typical SnapShot hardware configuration includes a Hitachi Simple

Modular Storage system, a host connected to the storage system and

software to configure and manage SnapShot (management software). The

host is connected to the storage system via iSCSI connections. The

management software is connected to the storage system via a

management LAN.

SnapShot employs primary volumes (P-VOLs), virtual volumes (V-VOLs),

data pool, and Hitachi Storage Navigator Modular 2 Graphical User

Interface. Advanced user functionality is available with Storage Navigator 2

Command-Line interface (CLI) and Hitachi Command Control Interface

(CCI). Figure 1-1 shows a typical SnapShot configuration.

SnapShot Overview 1–3

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

•

Figure 1-1: SnapShot functional components

The following sections describe how these components work together.

How SnapShot Works

SnapShot creates a virtual duplicate volume of another volume. This

volume “pair” is created when you:

• Select a volume that you want to replicate

• Identify another volume that will contain the copy

• Associate the primary and secondary volumes

• Create a snapshot of the primary volume data in the virtual (secondary)

volume.

Until the new or re-synchronized pair is split, all data written to the primary

volume is also copied to the virtual volume. When the pair is split, the

primary volume continues being updated, but the snapshot in the virtual

volume remains as it was at the time of the split. The pair can be made

identical again by re-synchronizing changes from primary-to-secondary or

secondary-to-primary.

1–4 SnapShot Overview

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Volume Pairs—P-VOLs and V-VOLs

A volume pair is a relationship established by SnapShot between two

volumes. A pair consists of a production volume, which contains the original

data and is called the primary volume (P-VOL), and from 1 to 32 virtual

volumes (V-VOLs), which contain copies of the P-VOL. The P-VOL and its V-

VOL(s) are located in the same Simple Modular Storage system.

A V-VOL is a mirror image of the P-VOL at the time of the snapshot. Unlike

the P-VOL, which contains the actual data, the V-VOL is made up of pointers

to the data.

To maintain the snapshot image of the P-VOL as new data is being written

to the P-VOL, SnapShot copies data being replaced to the data pool. V-VOL

pointers are updated to reference the original data's new location in the

pool. Figure 1-2 illustrates SnapShot volumes and data pool interaction.

SnapShot Overview 1–5

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

•

Figure 1-2: V-VOL Maintains SnapShot Data

1–6 SnapShot Overview

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Data Pools

After a snapshot, the V-VOL maintains a static copy of the P-VOL even as

new writes are updating the P-VOL. To do this, before an updated block is

written to the P-VOL, SnapShot sends the data that is being replaced to the

data pool. Pointers in the V-VOL are updated to locate the replaced data that

is now located in the data pool, thus maintaining the V-VOL point-in-time

image of the P-VOL.

The data pool’s function in the SnapShot process is illustrated in Figure 1-2.

Up to 64 data pools can be set for each controller. Each data pool can be

assigned to two or more P-VOLs plus the differential data of two or more V-

VOLs.

Differential Management LUs (DM-LU)

The DM-LU is an exclusive volume used for storing SnapShot information

when the array system is powered down. The DM-LU is treated the same as

other volumes in the storage system, but is hidden from a host. The DM-LU

is set at the factory at 10 GB. User configuration is not required

Consistency Group (CTG)

Application data often spans more than one volume. With SnapShot, it is

possible to manage operations spanning multiple volumes as a single group.

In a “consistency group” (CTG), all primary logical volumes are treated as

a single entity.

Managing SnapShot primary volumes as a consistency group allows

multiple operations to be performed on grouped volumes concurrently.

Write order is guaranteed across application logical volumes, since

snapshots can be taken at the same time.

SnapShot Interface—Storage Navigator Modular 2

Use Storage Navigator Modular 2 (Navigator 2) on the workstation to

perform SnapShot tasks. Configure, operate, and monitor SnapShot

functions with either of two interfaces: a graphical user interface (GUI) or a

Command Line Interface (CLI). Instructions in this guide refer to both

interfaces.

•

CAUTION! Storage Navigator 2 CLI is provided for users with significant

storage management expertise. Improper use of this CLI could void your

Hitachi Simple Modular Storage 100 system warranty. Please consult with

your reseller before using CLI.

Planning and Design 2–1

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

Planning and Design

A backup insures that a volume with bad or missing data can be

restored. With SnapShot you create copies of your production

data that can be used for backup and other uses.

Creating a backup system that fully supports business continuity

is best done when SnapShot is configured to match your business

needs.

This chapter guides you in planning a configuration that meets

organization needs and the workload requirements of your host

application.

 The Plan and Design Workflow

 Assessing Business Needs

 Establishing Data Pool Size

 Calculating Maximum Capacity

 Operating System Considerations

2–2 Planning and Design

Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide

The Plan and Design Workflow

The SnapShot planning effort consists of finding the number of V-VOLs your

organization requires for the P-VOL, the V-VOL(s)’ lifespan — how long they

must be held before being updated again — the frequency that snapshots

are taken, and the size of the data pool. The answers are determined by

analyzing the organization’s business needs and measuring the write

workload that is generated by the host application.

The plan and design workflow consists of the following:

• Assess business needs.

• Determine how often a snapshot should be taken.

• Determine how long the snapshot should be held.

• Determine the number of snapshot copies required per P-VOL.

• Measure production system write workload.

• Size the data pool. (For a description of the data pool, see Data Pools

on page 1-6.

These objectives are addressed in detail in this chapter. Two other tasks are

required before your design can be implemented. These are also addressed

in this chapter.

• When you have established your SnapShot system design, the system’s

maximum allowed capacity must be calculated. This has to do with how

the Storage system manages segments.

• Equally important in the planning process are the ways that various

operating systems interact with SnapShot. Make sure to review the

information at the end of the chapter.

Assessing Business Needs

Business needs have to do with how long back-up data needs to be retained

and what the business or organization can tolerate when disaster strikes.

These organizational priorities help determine the following:

• How often a snapshot should be made (frequency)

• How long a snapshot (the V-VOL) should be held (lifespan)

• The number of snapshots (V-VOLs) that will be required for the P-VOL.

Establishing How Often a Copy Is Made (Copy Frequency)

The frequency that copies need to be made is determined by how much data

can be lost in a disaster before business is significantly impacted.

To determine how often a snapshot should be taken

• Using knowledge of your business, decide how much data could be lost

in a disaster without significant impact to the business.

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Hitachi MK-97DF8018-00 User manual

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Model: MK-97DF8018-00

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